Bill English would have had a 'competitive' chance to beat Jacinda Ardern in 2020

Bill English has revealed his decision to vacate the National leadership had nothing to do with his own political relevancy going forward, saying he would have had a "competitive" chance to beat Jacinda Ardern in 2020.

"We'd certainly be aiming to win [in the 2020 general election]," Mr English said from the Beehive in Wellington this morning.

"Staying on would mean being totally committed to that, and I have no doubt that if I was totally committed to it I'd have the support of the caucus.

"So murmurings and speculation didn't have any influence on my decision."

He decided to leave during a relaxing period over Christmas with his family, without the impending worries of cabinet he had faced for the past nine years.

Mr English said he reasons for not stepping down straight after the election was concerns over the unfamiliar transition to the opposition role for his party.

"As a leader I wanted to make sure, what was a big change for my team of MPs and staff, that we got on with the job, make sure that we got organised as an opposition," Mr English said.

"Almost one in two New Zealanders had voted for us so we needed to reflect their concerns about the government.

"Then over the summer had a bit of time to thing about it, and then once you've decided to go I think it's always actually better to go. Otherwise it's bad for the group of people you're meant to be leading."

Mr English nevertheless admitted he did waver "backwards and forwards a bit" on the decision.

"There's always a reason to stay," he said.

"Politics, there's all this energy in it. Sometimes it's a bit negative but generally it really keeps you going, keeps you interested, there's a lot happening, there's a lot of momentum.

"For political reasons it'd be good to stick around, have a crack at this government because I think they're going to run into some real problems over the next couple of years.

"But in the end, as i said yesterday, it was a personal decision, not a political one, and I'm ready to go, looking forward to a new start with my family for whom politics have been their whole lives and we want to change that."

Mr English will leave the National leadership, and Parliament entirely on February 27.

He has not revealed who he will be voting for as next National leader.